1. Field of the Invention
The present invention relates to a novel organopolysiloxane composition capable of being vulcanized beginning at ambient or room temperature ("RTV") into an elastomer which is self-adhesive to the most diverse substrates, in particular to glass, wood and plastics such as polyvinylchloride (PVC). More particularly, the present invention relates to novel organopolysiloxane compositions presented in two-component or two-package form prior to use.
2. Description of the Prior Art
Organopolysiloxane compositions which are capable of being vulcanized beginning at ambient temperature are well known to this art and are divided into two separate RTV categories: single-component compositions and two-component or two-package compositions.
Single-component compositions cross-link when they are exposed to atmospheric moisture, typically in the absence of catalysts.
Contrariwise, two-component compositions are marketed and stored in the form of two separate components, a first component containing the polymeric base materials and the second component containing a catalyst. The two components are mixed extemporaneously at the time of use and the mixture cross-links into the form of a relatively hard elastomer.
These two-component compositions are well known to the art and are described, in particular, in the text by Walter Noll, Chemistry and Technology of Silicones, 2nd edition, pages 395 to 398 (1968) and in U.S. Pat. No. 2,843,555.
Such compositions incorporate essentially four (4) different ingredients:
(i) a diorganopolysiloxane having silanol end groups;
(ii) a cross-linking agent, typically a silicate or a polysilicate;
(iii) a tin catalyst; and
(iv) a filler.
Compared to the single-component compositions, the two-component compositions have the advantage of being less costly.
For some applications, they are easier to handle and can be cast, molded and cross-linked in situ at ambient temperature. However, they have the disadvantage of poorly adhering to various substrates such as glass, metals, wood, plastics, concrete, and the like. To overcome this disadvantage it has already been proposed to this art to apply, beforehand, to the substrates an adhesive primer layer to which, after drying, the organosiloxane composition is applied. Usual primers are, for example, a mixture of an alkoxysilane and a resin in organic solution. The use of these primers makes it necessary, however, to apply an additional material, which increases the overall costs.
Self-adhesive, two-component, organopolysiloxane compositions incorporating silanes containing an amine function have also been proposed to this art, in U.S. Pat. Nos. 3,801,572 and 3,888,815.
These silanes containing an amine function are broadly outlined. However, the prior art does not present the problem of, nor does it propose a solution to, providing a self-adhesive organopolysiloxane composition in two-component form which possesses the following desirable properties at the same time:
(a) marked adhesion to the most widely diverse substrates and particularly glass, metals, in particular aluminum, and plastics, in particular PVC, etc.;
(b) good "reversion" behavior. In fact, when these known elastomers of the above type are subjected to heating immediately or shortly after their preparation, for example 24 hours after the mixing of the diorganopolysiloxane, the cross-linking agent and the tin, a phenomenon referred to by those skilled in this art as "reversion" is frequently encountered, beginning in the middle of the cross-section of the elastomers. During this heating, the elastomers liquefy or soften internally, although most of the time they remain solid on their external surfaces; nevertheless, the relatively thin layer which remains under these conditions is frequently sticky. This "reversion" can already be produced at temperatures above 80.degree. C. However, in the majority of cases it is produced at temperatures above 100.degree. C., and it is particularly marked when the elastomers are heated in the total or virtual absence of air, that is to say, when the heated elastomers are in a partly or wholly closed system when being heated. Consequently, this "reversion" constitutes a very inconvenient disadvantage, in particular in certain applications in which the hardened elastomers are heated after cross-linking;
(c) complete and uniform cross-linking of the composition throughout its bulk at ambient temperature; and
(d) a rapid surface set.